Crimpable electrical connectors made of sink drawn tubing



C- A. KIRWIN May 16, 1967 GRIMPABLE ELECTRICAL CONNECTORS MADE OF SINK DRAWN TUBING Filed July 28, 1965 3 CHARLES g/( United States Patent 3,320,356 CRIMPABLE ELECTRICAL CONNECTORS MADE OF SINK DRAWN TUBING Charles A. Kirwin, Collinsville, IlL, assignor to Kearney- National Inc, St. Louis, Mo., a corporation of Delaware Filed July 28, 1965, Ser. No. 478,528 2 Claims. (Cl. 174-94) This invention relates to the manufacture of fittings for electric connections, and more particularly to tension sleeves of the type which are slipped over the ends of two conductors (to be connected end to end) and compressed to complete the electrical and mechanical connection.

U.S. Patent No. 2,244,109 discloses a method of manufacturing connector sleeves of this general type. According to that patent, the interior of a metal sleeve is sprayed with two metals, one, harder than the metal of the sleeve, for strength or gripping qualities, and the other, of high electrical conductivity, for conductivity. These materials are successively sprayed with two guns (an operation now commonly called metallizing) so that one side of the inner wall of the sleeve is covered with a hard metal for holding and the other side of the sleeve covered with a high conductivity metal. According to the patent, in order to insure that the spray material impinges the inside surfaces of the sleeve to make a good coating which adheres firmly to the inside surfaces of the sleeves, the spray must be directed at an angle to the longitudinal axis of the sleeve. Obviously, the angularity of the spray limits the length of the trajectory (within the sleeve) of the sprayed material. Hence, with sleeves having a length to orifice ratio much less than that illustrated in said patent, the depth (axially of the sleeve) to which the spray is projected, when the gun is angularly oriented, approaches the unsubstantial. Indeed, when the gun projects its stream in axial alignment with a sleeve whose length to orifice ratio is as low as that illustrated in the patent, it is next to impossible to achieve impingement with any substantial force for half the length of the interior unless the orifice be large enough to accommodate the nozzle of the gun. Consequently, much of the material sprayed into small bore tubes is ineffective through loss by failure to adhere.

Some improvement in the latter respect has heretofore been achieved by abrading the interior of the sleeve prior to, or concurrently with, the spraying, but forcible impingement of abradant on interior surfaces of the sleeve, and hence its effectiveness, is limited by the same factors which limit the trajectory of sprayed metal.

Accordingly, it is the general object of the present invention to obviate the aforesaid shortcomings of the prior practices.

It is also the object of this invention to provide a method of manufacture for a fitting of this kind which has fewer and more facile operations, and also results in a fitting which, when compressed, produces a metal to metal bond with a conductor having higher mechanical strength and lower electrical resistance than those heretofore available.

The present invention contemplates the manufacture of such compression fittings by a method which involves using, as a starting material, tubing drawn to produce an interior surface which (as drawn) is rough and wavy. Tubing with such an interior surface, hereinafter termed mill-rough, can be produced by the process known in the art of tube drawing as sink drawing, in which the tube is drawn through a drawing die without a plug, mandrel or the like, engaging the inside of the tube. Alternatively, tubing with such a mill-rough on the interior 3,320,356 Patented May 16, 1967 can be produced by the ordinary drawing process wherein a plug, mandrel, or the like, engages the interior of the tube, provided the mandrel be made with peaks or protuberances, and rotated, or otherwise moved, circumferentially relative to the tubing being drawn while the drawing process is in progress. In either event, the re sultant tubing is characterized as drawn by a mill-rough interior surface which is macroscopically undulating and rough.

The mill-rough concave surface of such tubing is in striking contrast with the almost perfectly smooth interior surface of ordinary mandrel-drawn tubing.

The mill-rough interior is further characterized by a pattern of undulation which has a herringbone type of configuration.

The mill-rough interior surface peculiarly adapts such tubing for use in the manufacture of compression fittings by providing roughness characterized by ridges which run athwart the axial direction of the fitting, and hence improves the mechanical grip between the fitting and the wire over fittings which are interiorly roughened by abrading.

If the tubing having a mill-rough interior surface is not in a crimp temper (i.e., for copper Rockwell F 45 or less) as drawn, it is annealed to crimp temper at some stage in the manufacture of the fittings from it.

Given such mill-rough tubing of crimp temper, and having an internal diameter averaging about 0.005 to 0.020 inch greater than the outside diameter of the wire with which it is to be used, all that is required, in accordance with the present invention, is that such tubing be cut to the lengths desired for the fittings to be produced. However, if desired, the cut lengths can be interiorly sprayed with metal, preferably the same metal of which the tubing is made. Such spraying can be done in accordance with the teaching of the aforesaid patent. If, subsequent to the drawing of the tubing, the interior thereof has become soiled, the cut lengths should be cleaned before they are metallized. Conventional cleaning and degreasing procedures which involve the use of hot carbon tetrachloride in a Blakeslee degreaser do not always satisfactorily clean the interior surface of tubing having mill-rough interior, but the familiar bright dip solutions, which are acidic, can clean the interior surfaces of cut lengths of copper tubing quite adequately. The cut lengths of copper tubing are immersed in such a bright dip solution for from ten to twenty seconds, removed, and rinsed with water. If it is desired to metallize the ineriors of the cut lengths, such metallizing is preferably done within less than eight hours after the cut lengths of tubing have been cleaned as aforesaid, unless, in the meantime, they have been protected from dust, oxidation, and other soiling agents.

In order to secure the best mechanical anchorage between the metal deposited on the interior of sink drawn tubing, the cut lengths are preheated \to a temperature in the range of 400 F. to 600 F., and immediately metallized. When so preheated and immediately me'tall-ized, the spray of molten metal may be composed of globules of larger magnitude than those which, according to prior practice, would adhere to the abraded surface on the interior of such tubes. While, with tubes having abraded interiors, it was conventional to employ a metallizing gun fed with one-eighth inch wire, it is preferable, in accordance with the present invention, to employ such a gun fed with three-sixteenths inch wire, which results in the production of larger globules of molten metal.

To illustrate the application of the process contemplated by this invention, a compression fitting for use with conductor wire having an outside diameter of 0.164 inch (plus or minus 0.008) will be described. Copper tubing of crimp temper having a mill-rough interior whose waviness or roughness is preferably at least 125 microinches (ASA Standards B46ll955), with an outside diameter of 0.312 inch, and an average inside diameter of 0.180 inch ($0.002 inch) is provided, it being understood that there may be peaks on the interior of the tubing which reduces the local diameter to less than the diameter of the wire, so that scratching occurs when the two are telescoped. Such tubing is cut to lengths of about 2.5 inches. The cut lengths of tubing are then immersed in a bright dip bath as aforesaid. Unless the cut lengths of tubing are extraordinarily soiled on the inside, it is sufiicient to dip them in the bath and immediately remove them, but the more extensive the soiling of the interiors, the longer the parts should remain in the bath. Upon removal of the parts from the cleaning bath, they are rinsed and then preheated in a suitable furnace to a temperature of between 400 F. and 600 F. Upon attaining a temperature of, for example, 400 F, the cut lengths of tubing are removed from the furnace and immediately metallized by spraying their interiors with copper, first from one end and then from the other. The spray is preferably addressed axially through the open ends of the cut lengths of tubing. As indicated above, it is preferable to deposit the copper on the interior of the cut lengths of copper tubing in the form of particles which are relatively large in comparison with previous practice, and this is accomplishable by the use of a metallizing gun employing three-sixteenths inch diameter copper wire. The metallizing reduces the internal diameter by a few thousandths of an inch.

When it is not intended to metallize the mill-rough interior of the connector, its internal diameter may range from 0.002 inch less than, to 0.020 inch greater than, the diameter of the wire for which it is intended, provided the average internal diameter of the tube is on the order of 0.005 to 0.010 inch greater than the average outside diameter of the wire.

At some suitable stage in the manufacture, which may be before the cut lengths of tubing are cleaned, or after they are metallized, or at any stage in between except between the preheating and the metallizing, the cut lengths of tubing are preferably formed with a circumferential indentation substantially midway between their ends, for the purpose of constricting the interior surface to a diameter less than the diameter of the wire with which the connector is intended to be employed.

In the accompanying drawing:

FIGURE 1 is a view in side elevation, partially in longitudinal section, of a connector sleeve made of sink drawn tubing in accordance with the present invention;

FIGURE 2 is a view in side elevation of a typical splice formed with a connector such as that shown in FIGURE lyand FIGURE 3 is a sectional view taken along the longitudinal axis of a section of connector having a mill-rough interior produced by sink drawing, and illustrating the roughness of the interior in section, as well as in elevation, between the oppositely disposed walls shown in section.

In the accompanying drawing, the fitting shown in FIGURE 1 is a connector sleeve 1 of the compression type used to splice the ends of copper wire conductors, and is formed of copper tubing having a mill-rough interior as above described. The sleeve 1 is constricted by a circumferential band 2 which reduces the internal diameter sufiiciently in this zone to prevent a conductor end 3 or 4 from passing more than halfway through the sleeve. 7

In use, a conductor end is inserted at each end of sleeve 1, and the sleeve parts endwardly of constriction 2 are then compressed by suitable tool at spaced intervals, in order to clamp the sleeve to the conductor ends 3 and 4 and form a splice in a manner well understood and common in the art.

From the foregoing description, those skilled in the art should understand the invention and realize that it accomplishes its objects.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. As an article of manufacture, a connector for splicing electrical conductors by crimping the connector onto the conductors. said connector comprising a sink drawn copper sleeve having a conductor stop intermediate its ends.

2. The connector of claim 1 wherein the internal surface of said sleeve is coated with adherent copper particles.

References Cited by the Examiner UNITED STATES PATENTS 2,038,535 4/ 1936 Brenizer. 2,576,528 11/1951 Matthysse 174-94 2,742,946 4/ 1956 McGrann 295 16 X LEWIS H. MYERS, Primary Examiner.

D. L. CLAY, Assistant Examiner. 

1. AS AN ARTICLE OF MANUFACTURE, A CONNECTOR FOR SPLICING ELECTRICAL CONDUCTORS BY CRIMPING THE CONNECTOR ONTO THE CONDUCTORS, SAID CONNECTOR COMPRISING A SINK DRAWN COPPER SLEEVE HAVING A CONDUCTOR STOP INTERMEDIATE ITS ENDS. 